Plants Do Math to Survive the Night

Plants use a chemical calculator to divide their amount of stored energy by the length of the night and thereby solve the problem of how to portion out their energy reserves overnight.

Biologists from the John Innes Centre in England discovered that plants have a biological process which divides their amount of stored energy by the length of the night. This solves the problem of how to portion out energy reserves during the night so that the plant can keep growing, yet not risk burning off all its stored energy.

While the sun shines, plants perform photosynthesis. In this process, the plants convert sunlight, water and carbon dioxide into stored energy in the form of long chains of sugar, called starch. At night, the plants burn this stored starch to fuel continued growth.

“The calculations are precise so that plants prevent starvation but also make the most efficient use of their food,” study co- author Alison Smith said in press release. “If the starch store is used too fast, plants will starve and stop growing during the night. If the store is used too slowly, some of it will be wasted.”

To give the foliage a math quiz, the biologists shut off the lights early on plants that had been grown with 12-hour days and nights. Plunging the plants into darkness after only an 8-hour day forced them to adjust their normal nightly rhythm. Since the plants didn’t have time to store as much starch as usual, they had to recalculate their metabolism.

Even after this day length trickery, the plants aced their exams and ended up with just a small amount of starch left over in the morning. They had neither starved, nor stored starch that could have been used to fuel more growth.

The plants weren’t doing anything consciously. Instead, chemical reactions did the number crunching automatically. The results of the study will be published in eLife, and can currently be read via the Cornell University Library.

The authors suggested that similar biological calculators may explain how a migratory bird, the little stints (Calidris minuta) can make a 5000-kilometer journey to their summer habitat in the Arctic and arrive with enough fat reserves to survive only approximately half a day more, on average.